The synthesis of thiophene from C.sub.4 raw materials such as furan, crotonaldehyde, butanol or butane, and sulphur compounds such as carbon disulphide, hydrogen sulphide and sulphur, may be accompanied by the formation of C.sub.4 mercaptans (primary or secondary butyl mercaptan) which it is difficult to separate by distillation because their boiling points are close to that of thiophene. Furthermore, the presence of small quantities of mercaptans may modify the olfactory properties of commercial thiophene, and is therefore undesirable.
It is known to purify hydrocarbons containing sulphur impurities by adsorption on sieves, resins and adsorbents of various types. It is also known to oxidize the mercaptans contained in the hydrocarbons using air or oxygen. Unfortunately, these techniques cannot be employed for thiophene since it can itself be oxidized to form sulphoxides and/or sulphones.
Other techniques may also be used, for example solvent extraction, in particular using an aqueous sodium hydroxide solution. However, further to its poor efficiency and the need to use a large excess of sodium hydroxide which cannot be recycled, use of this method would lead to the formation of polluted aqueous effluents.